Standalone automation control device is widely used as control device for small range process control in industry. Normally, it contains several input/output ports and configurable common process control algorithm (such as PID). After input/output ports are connected to field signals and process control algorithm is configured, a user can establish control loops and control process variables for a desired set point.
Almost all the standalone automation control devices use LED indicators on a control panel to show some information such as alarms, operation status, etc. However, most of the LED indicators simply comprise some lights with printed characters. The printed characters are difficult to read if the environment is dim or light is insufficient which is very likely to be the case because industrial automation control devices are frequently used under such environment. Moreover, the buttons on the panels are also difficult to be identified in a dim environment. Although some buttons on the control panels may be lighted up when they are in operation in the prior art, they are not lighted up until being pressed by user. As a result, it is also difficult for user to identify the buttons in a dim environment before the buttons are operated. These disadvantages cause inconvenient operation and increase possibilities of mis-operation, and then impact process control results.